Mr Hong said China urged the US to stop such surveillance missions, which he said endangered Chinese security in the air and sea.

The Pentagon said two Chinese J-11 fighters flew within about 15 metres of the EP-3 Aries on Tuesday, forcing the US pilot to descend sharply to avoid a collision. It said the US plane was conducting routine operations in international airspace.

It described the incident as an unsafe intercept and said it is being reviewed.

Mr Hong said: "According to the related Chinese authorities, the US allegation is not true. We urge the US to immediately stop spying activities and prevent such events from happening again."

The US has sought to prevent such confrontations through frequent communication and the signing of an agreement on handling unexpected encounters at sea and in the air.

However, such incidents may now be on the increase as the US challenges China's claims that its newly-created artificial islands in the South China Sea enjoy legal rights to territorial seas and airspace. China says it is entitled to keep watch over such airspace and seas.

China has long been irked by US reconnaissance missions off the Chinese island province of Hainan, which sits at the northern end of the South China Sea and is home to a number of highly sensitive naval and air installations.

In 2001, a collision between a Chinese fighter jet and a US surveillance plane in which the Chinese pilot was killed and the American crew detained on Hainan led to a crisis in US-China relations.